Neutral atom trapping device

ABSTRACT

A neutral atom trapping device with a multipole-magnetic field-generating electrode is provided with a main current electrode through which main current flows, and a pair of sub-current electrodes through which sub-current flows, and which is located in parallel to and both sides of said main current electrode; a neutral atom trapping device with an S-shaped multipole-magnetic field-generating electrode-.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a neutral atom trapping device, and inparticular to a neutral atom trapping device which specializes amultipole-magnetic field-generating electrode in a magneto-optical trapor/and a magnetic trap to enhance a magnetic quadrupole component whileattenuating a magnetic hexapole component in the region where neutralatoms are captured, so that neutral atoms can be effectively captured,and which reduces an applied current and/or an external magnetic fieldby generating the magnetic field, thereby enabling miniaturization ofthe whole device.

2. Description of the Related Art

Magneto-optical trap [MOT] is a publicly-known technology in the fieldof atom optics. By using a magneto-optical trap, neutral atoms can becaptured by irradiating laser beams of well-adjusted oscillatingfrequency along the axis of symmetry of the magnetic field lines in aquadrupole magnetic field. Since a magneto-optical trap can captureneutral atoms in the central region thereof and simultaneously performthe laser cooling, it is used as a method of cooling for most of theexperiments in the field of atom optics including the Bose-Einsteincondensate-generation experiment.

Generally, a quadrupole magnetic field in a magneto-optical trap isgenerated using anti-Helmholtz coils which are formed by placing a pairof circular coils opposite each other. However, as will be describedbelow, a quadrupole magnetic field can also be generated by superposinga magnetic field, which is generated by an electric current flowingthrough a single linear wire, on a uniform bias magnetic field.

FIGS. 1( a) and 1(b) are conceptual diagrams showing relationshipsbetween an electric current and a magnetic field. FIG. 1( a) is adrawing showing a condition of a magnetic field when an infinite linearcurrent (I) flows along an electrode (1) on the z-axis, while FIG. 1( b)is a drawing showing a condition of a magnetic field when a uniform biasmagnetic field is further applied in the positive (+) direction on thex-axis. As shown in FIG. 1( a), when the infinitely long linear current(I) flows along the electrode (1) on the z-axis, a concentric circularmagnetic field is generated around the linear current (I) due toAmpere's law. The magnetic flux density of the magnetic field thusgenerated is indicated by the following equation (i):

$\begin{matrix}{{B_{x} = {{- \frac{\mu_{0}I}{2\pi}}\frac{y}{x^{2} + y^{2}}}},{B_{y} = {\frac{\mu_{0}I}{2\pi}\frac{x}{x^{2} + y^{2}}}},{B_{z} = 0}} & (i)\end{matrix}$

In the equation (i), μ_(o) indicates the magnetic permeability ofvacuum. By adding a uniform bias magnetic field B_(ox) in the positive(+) direction on the x-axis, the flux density is indicated by thefollowing equation (ii):

$\begin{matrix}{{B_{x} = {{{- \frac{\mu_{0}I}{2\pi}}\frac{y}{x^{2} + y^{2}}} + B_{0x}}},{B_{y} = {\frac{\mu_{0}I}{2\pi}\frac{x}{x^{2} + y^{2}}}},{B_{z} = 0}} & ({ii})\end{matrix}$

It is seen from the equation (ii) that the zero-point of the magneticfield is formed at the point (0, μ₀I/(2π B_(0x)), 0) on the y-axis. Thezero-point is represented by ‘Q’. The distributed magnetic field linesin this condition are schematically illustrated in FIG. 1( b). As seenin FIG. 1( b), the zero-point Q of the magnetic field forms a quadrupolemagnetic field. Neutral atoms can be captured at the zero-point Q on thequadrupole magnetic field and the laser cooling can be performed.

In fact, neutral atoms can be captured three dimensionally by furtheradding a quadrupole magnetic field in the z-direction. FIGS. 2( a)-2(c)are conceptual diagrams showing configurations for adding a quadrupolemagnetic field in the z-direction and the conditions of the magneticfield. FIG. 2( a) shows an example in which a magnetic field isimpressed from outside using, for instance, anti-Helmholtz coils in thez-direction; FIG. 2( b) shows an example in which a path of electriccurrent is deformed to a U-shape by forming both ends of the coils intoa U-shape; and FIG. 2( c) shows an example in which a path of electriccurrent is deformed to a Z-shape by forming both ends of the coils intoa Z-shape. In other words, while it is preferable that a requiredmagnetic field is added from outside by using, for instance,anti-Helmholtz coils in the z-direction as shown in FIG. 2( a), in orderto generate a required magnetic field in the z-direction, since arequired magnetic field in the z-direction can be provided from the armportions parallel to the x-axis, by modifying both ends of the conductorwhere electric current flows to a U-shape as shown in FIG. 2( b), thistype is used more frequently than that of FIG. 2( a) (See e.g.non-patent document 1 below). However, in the method shown in FIG. 2(b), since the arm portions parallel to the x-axis also generate a biasmagnetic field in the y-direction, a bias magnetic field in they-direction has to be newly added externally in order for thecompensation.

In addition, in order for a general magneto-optical trap to cool theatoms three dimensionally, laser lights are irradiated from sixdirections along the axis of symmetry on a magnetic field towards thecentral portion of the trap which is composed of a quadrupole magneticfield generated by anti-Helmholtz coils, etc. It is known, however, thatmagneto-optical traps composed of a linear current and a bias magneticfield include one in which a total reflection mirror for the laserlights is placed on the x-z plane, and requiring merely four leaserlights instead of six as required originally by reusing the leaserlights reflected by the total reflection mirror. Such a magneto-opticaltrap is called a “Surface magneto-optical trap”, a “Mirrormagneto-optical trap”, or a “Mirror MOT”, and is often used as a compactmagneto-optical trap. It is to be noted that the method in which sixlaser lights are directly irradiated to a proximity of a conductorwithout using a mirror is called a “Wire trap”.

A modified configuration of a linear current to a Z-shape as in FIG. 2(c) can generate a magnetic field with a curvature in the z-axisdirection from the two arms parallel to the x-axis. Herein, “a magneticfield with a curvature in the z-axis direction” indicates aspace-dependent magnetic field in which the magnitude of the magneticfield B on the z-axis is proportional to z². The magnetic field thusobtained can steadily capture neutral atoms since a confinementpotential in the z-axis direction becomes a harmonic type beingproportional to z². However, a magneto-optical trap cannot be composedon this magnetic field since the z component of the magnetic field facesthe positive (+) direction of the z-axis everywhere in the magneticfield. Namely, a configuration with the magnetic field as described inFIG. 2( c) is used as a “magnetic trap” which can only capture neutralatoms without using the laser light. Generally, a magnetic trap composedby superposing a quadrupole magnetic field on the x-y plane and amagnetic field with a curvature in the z-axis direction is called a“Ioffe-Pritchard type magnetic trap”, and a rod-shaped conductor whichis provided in parallel to the x-y plane is called a “Ioffe bar”. Amagnetic trap, along with a magneto-optical trap, is an indispensabledevice in the field of atom optics research.

Three different types of the surface magneto-optical traps and thesurface magnetic trap indicated in FIGS. 2( a)-2(c) have a commonalitythat they generate a quadrupole magnetic field on the x-y plane bysuperposing a magnetic field with a narrow linear conductor forproviding electric current onto a uniform bias magnetic field formoutside; and since they can capture atoms in the extreme vicinity of aplane substrate, their application possibilities, such as in an atominterferometer, a quantum gate, and the like have been attractingattention, and researches have been actively performed.

Meanwhile, as indicated in FIG. 1( b), a quadrupole magnetic fieldgenerated by superposing a magnetic field generated by a single narrowlinear conductor onto a uniform external bias magnetic field becomesconsiderably asymmetrical as distanced away from the center of the trap,thereby deviating from an ideal quadrupole magnetic field. If amagneto-optical trap is composed by using such a magnetic field, thereis a problem that the effective capacity in the space where atomsdrifting in the vacuum are captured becomes limited, so that sufficientnumbers of atoms cannot be captured.

FIG. 3 is a conceptual diagram showing the condition of a threedimensional magnetic field wherein the width of a linear conductor inFIG. 2( b) is enlarged in the x-direction. As shown in FIG. 3, when thewidth of the linear conductor shown in FIG. 2( b) is enlarged in thex-direction, the uniformity of the magnetic field around the conductorincreases, so that the far-field magnetic profile is improved and thequadrupole reaches further away. As a result, an effective capacitywhere atoms can be captured is enlarged, so that a greater number ofatoms can be captured (see non-patent document 2 below). However, evenwhen such a plate conductor is used, a magnetic distortion cannot becompletely compensated, and an extra electric current has to be flowedthrough in proportion to the widened portion of the conductor.Therefore, the amount of heat generated from a conductor part isincreased. Since a magneto-optical trap and a magnetic trap are placedin an ultrahigh vacuum device, there may be a situation where gas isemitted from a surface of a conductor when the amount of heat generatedis increased, which is not desirable.

Also, a configuration with a Z-shaped conductor as shown in FIG. 2( c)is used for composing a magnetic trap which does not use the laserlight, so that a magnetic field does not have to be strictly uniformed.However, a relatively large bias magnetic field has to be applied inorder to capture atoms reliably. Furthermore, since the two Ioffe barsextending in the x-direction from both ends of the central conductor arerelatively long, an unnecessarily large z-directed bias magnetic fieldis generated, so that in order to compensate said bias magnetic field, alarge z-directed bias magnetic field has to be further added fromoutside. Accordingly, there is a problem that the whole device cannot beminiaturized even when a magnetic trap with a Z-shaped conductor show inFIG. 2( c) is used.

[Non-patent document 1] J. Reichel, W. Hänsel and T. W. Hänsch, “Atomicmicromanipulation with magnetic surface traps,” Phys. Rev. Lett. 83,3398 (1999).[Non-patent document 2] S. Wildermuth, P. Krüger, C. Becker, M. Brajdic,S. Haupt, A. Kasper, R. Folman and J. Schmiedmayer, “Optimizedmagneto-optical trap for experiments with ultracold atoms nearsurfaces,” Phys. Rev. A 69, 030901(R) (2004).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide magneto-opticaltraps and/or magnetic traps which are able to provide a larger capacityfor a region where neutral atoms are captured than the prior art.

It is an object of the present invention to provide magneto-opticaltraps and/or magnetic traps which can capture a greater number ofneutral atoms than the prior art.

It is an object of the present invention to provide magneto-opticaltraps and/or magnetic traps which can capture neutral atoms moreeffectively with lesser electric current than the prior art.

It is an object of the present invention to provide magneto-opticaltraps and/or magnetic traps which can further reduce gas emission due toheat generation than the prior art.

It is an object of the present invention to provide magneto-opticaltraps and/or magnetic traps which can further miniaturize the wholedevice than the prior art.

The first aspect of the present invention is based upon knowledge thatin a surface magneto-optical trap in which neutral atoms are capturedand cooled in the proximity of a surface of a substrate by using amagnetic field generated on the surface of a substrate by applying alinear current and an externally supplied bias magnetic field as well aslaser beams, a greater number of atoms can be captured in a surfacemagneto-optical trap by modifying a composition of a single narrowlinear conductor in the prior art to that of three narrow linearconductors aligned in parallel to each other; so that a magneticquadrupole component is reinforced while a magnetic hexapole componentis effectively cancelled out, thereby obtaining a more uniform magneticquadrupole field than the prior art, as well as enlarging the capacityof space where neutral atoms are captured.

Also, another embodiment of a neutral atom trapping device according tothe first aspect of the present invention is based upon knowledge thatthe same effect can be expected by adding an additional linear conductorabove the capturing region.

The second aspect of the present invention is based upon knowledge thatin a surface magneto-optical trap in which neutral atoms around thesurface of a substrate are captured using a magnetic field composed of aZ-shaped conductor on the surface of a substrate and a bias magneticfield supplied from outside, by further bending Ioffe bars of Z-shapedconductor in a right angle to form an S-shaped structure, a biasmagnetic field component generation in the z-direction can be reduced,the curvature at a z-directed magnetic field can be increased, a biasmagnetic field in the x-direction can be enhanced, thereby obtainingability to acquire the same atom capturing capability as that of theneutral atoms can be captured with lesser electric current than theprior art.

The present invention is based upon knowledge in which the whole devicecan be further miniaturized than the prior art by adopting all of theabove configurations. Specifically, by combining a configurationadopting three linear conductors (or a linear conductor added above thecapturing region) and a configuration adopting an S-shaped Ioffe bar,the capability of effectively capturing neutral atoms with less electriccurrent is enhanced, thereby a whole device is miniaturized.

A neutral atom trapping device according to the first aspect of thepresent invention is basically provided with a multipole-magneticfield-generating electrode which includes; an electrode for main currentwhere a main current flows, and a pair of sub-current electrodes, wherea sub-current flows, located in parallel to both sides of said electrodefor main current. As shown in FIG. 6 and in examples which will be laterdescribed theoretically, said sub-current electrodes function to enhancea magnetic quadrupole component while attenuating a magnetic hexapolecomponent in the region where neutral atoms are captured. “The regionwhere neutral atoms are captured” means a region where neutral atoms canbe captured in a neutral atom trapping device such as a magneto-opticaltrapping device, a magnetic trapping device, or the like and is a regionincluding the zero-point Q as will be described below.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein each of said maincurrent electrode and said pair of sub-current electrodes includes alinear portion. It is preferable that said linear portions are parallelto each other, and preferably three linear portions exist on the x-zplane. Moreover, said main current electrode and said pair ofsub-current electrodes preferably include a linear portion around thevicinity where neutral atoms are captured. By using themultipole-magnetic field-generating electrodes with such an embodiment,a magnetic field where neutral atoms can be effectively captured can beformed.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein each of said maincurrent electrode and said pair of sub-current electrodes includes alinear portion, and the linear portion in said main current electrodeand the linear portion in said pair of sub-current electrodes areelectrically interconnected with connecting portions which extend in avertical direction to the electrodes. By using the electrodes accordingto such an embodiment, it can be utilized as an S-shaped electrode whichwill be later described, so that neutral atoms can be effectivelycaptured and the whole device can be miniaturized.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein each of said maincurrent electrode and said pair of sub-current electrodes includes alinear portion; the linear portion in said main current electrode andthe linear portion in said pair of sub-current electrodes areelectrically interconnected with connecting portions which extend in avertical direction to the electrodes; positions where said twoconnecting portions and said main current electrode intersect are set onopposite sides of a position of said main current electrodecorresponding to a central position where the neutral atoms arecaptured. By using the electrodes according to such an embodiment, itcan be utilized as an S-shaped electrode which will be later described,so that neutral atoms can be effectively captured and the whole devicecan be miniaturized.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein one or more ofsaid main current electrode and said pair of sub-current electrodesinclude: a linear portion; and portions bending downwards (in a negativedirection of the y-axis) at one or both ends of said linear portion.Having the portions bending downwards, it is made possible to enhance anx-directed bias magnetic field at the vicinity of the zero point, sothat an external magnetic field can be reduced, and it is consequentlymade possible to reduce applied current for a device while miniaturizingthe whole device.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein one or more ofthe said main current electrode and said pair of sub-current electrodesinclude: a linear portion; and a U-shaped portion having a linearportion and bending portions at both ends of said linear portion. SuchU-shaped portions are provided on the x-z plane, and one including twolinear portions parallel to the x-axis and a linear portion parallel tothe z-axis while connected to said portions parallel to the x-axis canbe mentioned. Since it includes such electrode portions, a z-directedmagnetic field can be enhanced by a magnetic field generated by theportions parallel to the x-axis, so that an external magnetic field isreduced, and it is consequently made possible to reduce applied currentfor a device while miniaturizing the whole device.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices having an optical beamgenerating portion for irradiating optical beams into a multipolemagnetic field generated by said multipole-magnetic field-generatingelectrode. Having an optical beam generating portion, the neutral atomtrapping device can function as so-called “magneto-optical trap”. It isto be noted that publicly-known elements in magneto-optical traps andmagnetic traps can be appropriately adopted for the neutral atomtrapping device of the present invention. The neutral atom trappingdevices themselves are publicly-known, and may appropriately include:vacuum pumps for vacuum device, a vacuum chamber with electrode storagecapacity, an atom-beam generating portion which generates neutral atoms,a magnetic field generating portion (electrode) for applying variousmagnetic fields, mirrors, detectors, and the like. When the neutral atomtrapping device of the present invention is used to deposit neutralatoms on samples, a sample stand for loading samples, a control devicefor controlling the position of a sample stand, an electric fieldgenerating device for controlling directions of atom beams, a magneticfield generating device for controlling directions of atom beams, alight source for controlling directions of atom beams, and the like maybe appropriately included.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices which is provided with: anoptical beam generating portion for irradiating optical beams from fourdirections along a symmetric axis of a magnetic quadrupole componentinto a multi-pole magnetic field generated by said multipole-magneticfield-generating electrode; and a total reflection mirror; and whichfunctions as a surface magneto-optical trap.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices which has an optical beamgenerating portion for irradiating optical beams from six directionsalong a symmetric axis of a magnetic quadrupole component into amultipole magnetic field generated by said multipole-magneticfield-generating electrode without having a total reflection mirror.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is provided with: amultipole-magnetic field-generating electrode which includes; a maincurrent electrode where a main current flows; and a sub-currentelectrode which is provided on an opposite side of said main currentelectrode through a region where neutral atoms are captured and whichincludes a linear portion where a sub-current flows. The neutral atomtrapping device of this embodiment also functions in the same way asdescribed above, so that the sub-current electrode enhances the magneticquadrupole component while attenuating a magnetic hexapole component. Itis to be noted that the neutral atom trapping device according to thisembodiment can appropriately adopt each arrangement mentioned above. Amore preferred embodiment of a neutral atom trapping device according tothis embodiment is a neutral atom trapping device, wherein saidsub-current electrode includes a linear portion which is provided abovesaid main current electrode through a region where neutral atoms arecaptured, curved portions extending downwards from both ends of saidlinear portion; and a linear portion extending downwards from saidcurved portions. More specifically, it is any one of the above-mentionedneutral atom trapping devices, wherein said sub-current electrodeincludes: a linear portion which is provided above said main currentelectrode through a region where neutral atoms are captured;semicircular portions extending downwards from both sides of said linearportion; and linear portions extending downwards from bottom ends ofsaid semicircular portions. Such a curved portion and a semicircularportion contribute(s) to generating a z-directed magnetic field besideseffectively detouring a laser light. Furthermore, the portion extendingdownwards contributes towards generating an x-directed magnetic field.Thus, since an external magnetic field can be reduced, the whole devicecan be miniaturized besides reducing current applied to the device.

A neutral atom trapping device according to the second aspect of thepresent invention is provided with: when a point of origin is set at apoint below a central region where neutral atoms are captured, a z-axisis set to a direction of the linear portion of a multipole-magneticfield-generating electrode near a center where said neutral atoms arecaptured and a center where the neutral atoms are captured is providedon the y-axis, said multipole-magnetic field-generating electrodeincludes; a linear portion extending along the z-axis through said pointof origin; a portion extending in a direction parallel to the x-axisfrom said linear portion; and a portion parallel to the z-axis extendingfrom the two portions extending in a direction parallel to the x-axis.As described above, by forming an S-shaped structure by further bendingthe Ioffe bar of a Z-shaped conductor in right angle, generation of az-directed bias magnetic field component can be reduced whilereinforcing the curvature in a z-directed magnetic field, as well asreinforcing an x-directed bias magnetic field. As a result, it is madepossible to obtain the same degree of ability to capture neutral atomswith lesser electric current than the prior art.

According to the present invention, magneto-optical traps and/ormagnetic traps which are able to provide a larger capacity for a regionwhere neutral atoms are captured than the prior art can be provided.Therefore, according to the present invention, magneto-optical trapsand/or magnetic traps which can capture a greater number of neutralatoms than the prior art can be provided.

According to the present invention, it can provide magneto-optical trapsand/or magnetic traps which can capture neutral atoms more effectivelywith lesser electric current than the prior art can be provided.Therefore, according to the present invention, magneto-optical trapsand/or magnetic traps in which can further reduce gas emission due toheat generation than the prior art can be provided.

According to the present invention, magneto-optical traps and/ormagnetic traps which can further miniaturize the whole device than theprior art can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) and 1(b) are conceptual diagrams showing a relationshipbetween an electric current and a magnetic field. FIG. 1( a) is adrawing showing a condition of a magnetic field wherein aninfinitely-long linear current (I) flows along the z-axis, while FIG. 1(b) is a drawing showing the condition of a magnetic field wherein anuniform bias magnetic field is further applied in the positive (+)direction on the x-axis.

FIGS. 2( a)-2(c) are conceptual diagrams showing a configuration inorder to add a quadrupole magnetic field in the z-direction and thecondition of the magnetic field. FIG. 2( a) shows an example in which amagnetic field is applied towards the z-axis from outside using, forinstance, anti-Helmholtz coils. FIG. 2( b) shows an example in which apath of electric current is deformed to a U-shape by forming both endsof the linear conductor into a U-shape. FIG. 2( c) shows an example inwhich a path of electric current is deformed to a Z-shape by formingboth ends of the linear conductor into a Z-shape.

FIG. 3 is a conceptual diagram showing the condition of a threedimensional magnetic field wherein the width of a linear conductor inFIG. 2( b) is enlarged in the x-direction.

FIG. 4 is a pattern diagram illustrating the principle of a neutral atomtrapping device according to the first aspect of the present invention.

In FIGS. 5( a)-5(c), a magnetic field (FIG. 1( a)) formed by a singlelinear current I₁ near the trap center (the zero point Q) is expandedinto multipoles, in which magnetic multipole components of dipole,quadrupole and hexapole are schematically illustrated. FIG. 5( a) showsthe condition of a dipole magnetic field; FIG. 5( b) shows that of aquadrupole magnetic field, FIG. 5( c) shows that of a hexapole magneticfield.

FIG. 6 schematically represents an overlapping view of the quadrupolemagnetic field with the hexapole magnetic field generated around thetrap center Q (0, y0) by electric current I₁ flowing through the centralconductor.

FIG. 7 is a conceptual diagram showing an example of a wiring which doesnot block the leaser beams.

FIG. 8 is a conceptual diagram showing a new conductor in which botharms (the Ioffe bars) extending towards the x-axis, which is used oftenfor surface magnetic traps in a conventional Z-shape conductor, are bentin the z-direction.

FIG. 9 is a conceptual diagram showing an example in which a pair ofsub-current electrodes (conductor) flowing through I₂ in the firstaspect of the present invention of a neutral atom device also serves asPart C in the second aspect of the present invention of a neutral atomdevice.

FIG. 10 is a conceptual diagram of a surface magneto-optical trap.

FIGS. 11( a) and 11(b) are graphs showing the calculation resultcomparing the structure of two-dimensional magnetic field generated bythe main current I₁ alone, with that generated by the cancellationprocess of the hexapole magnetic field when both the main current I₁ andthe sub-current I₂ are used. FIG. 11( a) shows a magnetic fieldgenerated by the main current I₁ alone, FIG. 11( b) shows the conditionof the two-dimensional magnetic-field structure generated by completelycanceling the hexapole magnetic field using the main electric current I₁together with the subsidiary electric current I₂.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Configuration inwhich Sub-Currents are Placed on Both Sides of Main Current]

FIG. 4 is a pattern diagram illustrating the principle of a neutral atomtrapping device according to the first aspect of the present invention.‘2’ in FIG. 4 represents a main current electrode while ‘3’ representssub-current electrodes. As shown in FIG. 4, a neutral atom trappingdevice according to the first aspect of the present invention can obtaina more uniform quadrupole magnetic field than the prior art modifying acomposition of a single narrow linear conductor in the prior art to thatof three narrow linear conductors aligned in parallel to each other;thereby reinforcing a magnetic quadrupole component while effectivelycanceling out a magnetic hexapole component; as a result obtaining amore uniform magnetic quadrupole field than prior art.

A neutral atom trapping device according to the first aspect of thepresent invention is basically provided with: a multipole-magneticfield-generating electrode with a main current electrode (2), and a pairof sub-current electrodes (3) through which the sub-current flows, andwhich is located in parallel to and both sides of said main currentelectrode. As will be described theoretically in the execution examplelater, said sub-current electrodes function to enhance a magneticquadrupole component while attenuating a magnetic hexapole component inthe region where neutral atoms are captured. “The region where neutralatoms are captured” means a region where neutral atoms are to becaptured in a magneto-optical trap and/or a magnetic trapping devicesuch as a region comprising the zero-point Q as explained below. Theparameters for the region where neutral atoms are captured are set at,for instance, 1 mm-10 cm above the main current electrode, or preferablyat 1 mm-1 cm, or more preferably at 2 mm-1 cm.

As materials used for each electrode, metals, metallic oxides,conductors, superconductors, or the like can be used appropriately. Asfor the materials which can be used under normal temperature—from thestandpoint of reducing heat generation, since the electric resistance isdesirably as small as possible, metal materials with the electricresistance of the order of 10⁻⁸ Ωm, (specifically at 1×10⁻⁸ Ωm-1×10⁻⁷Ωm), such as gold, silver, copper, aluminum, and the like are preferred.However, a region where transparency to laser beams is especially ofimportance, a transparent conducting oxide such as ITO with the electricresistance value of the order of 10⁻⁶ Ωm (specifically 1×10⁻⁶ Ωm-1×10⁻⁵Ωm) can also be used. “A region where transparency to laser beams isespecially of importance” means, for instance, a part where the opticallaser passes through and/or an electrode part which is located near theregion where the optical laser passes through. Specifically, in the casethere is a circumstance in which an electrode for sub-current is placedabove the trapping region of neutral atoms; then, there is acircumstance in which an electrode for sub-current is designed as atransparent electrode. In addition, a superconductor can be used in thecase there is a circumstance in which a vacuum device comprises astructure enabling to cool below the temperature of liquid nitrogen.However, in general, since there is an upper limit value in an electriccurrent which can be applied to a superconductor, it is not always thecase that superconductors are preferred.

As for the magnitude of a quadrupole magnetic field forcapturing/cooling neutral atoms, it ranges: 1×10⁰ G/cm˜1×10³ G/cm, andit can also be 1×10⁰ G/cm˜1×10² G/cm, or 5×10⁰ G/cm˜5×10² G/cm. Forexample, in the case of the magnitude of a quadrupole magnetic field ina MOT for rubidium atoms, 5×10⁰ G/cm˜5×10² G/cm can be mentioned, wherespecifically approximately 10 G/cm can be mentioned.

Accordingly, when the trapping region of neutral atoms is formed severalmillimeters away from the main current electrode, 5-10 A can bementioned as the value of the main current, and 10-20 A can be mentionedas the value of each of the pair of sub-currents. Also, given that thevalue of a main current is set as I₁ and that of a sub-current as I₂,then 1-3 can be mentioned as the value of I₂/I₁, or it may be 1.5-2.5,it may be 3.5-4.5, preferably 3.5-4.0. Thus, the sub-current ispreferably larger than the main current, while directions of both of themain current and the sub-current may be the same or opposite, as will bedescribed later in theoretical calculations, the same direction ispreferable. The length of both electrodes for main and sub-current canadopt the publicly-known length in a MOT.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein a linear portionis provided in both said main current electrode and said pair ofsub-current electrodes. While it is preferable that the linear portionis as lengthy as possible, it is preferable that at least there is alinear portion in the entire region where neutral atoms are captured. Inaddition, it is preferable that said linear portions are parallel toeach other, and preferably the three linear portions exist on the x-zplane. Moreover, said main current electrode and said pair ofsub-current electrodes are preferably provided with a linear portionaround the vicinity where neutral atoms are captured. By utilizing amultipole-magnetic field-generating electrode according to such anembodiment, it is made possible to generate a magnetic field whereneutral atoms can be effectively captured. It is to be noted thataccording to the specification of the present invention, the vicinity oftrapping region where neutral atoms are captured, the coordinates are soestablished that the direction to which a main current flows is set asthe direction of the z-axis while the central portion of the trappingregion where neutral atoms are captured is set at a point on the y-axis.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein: each of saidmain current electrode and said pair of sub-current electrodes has alinear portion; and the linear portions of both said main currentelectrode and said pair of sub-current electrodes are electricallyconnected at the connecting portions which extend in the verticaldirection to the electrodes. By using the electrode according to such anembodiment, since it can also be used as the later described S-shapedelectrode as shown in FIGS. 8 and 9, it can capture neutral atomseffectively and also miniaturize the whole device.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein each of said maincurrent electrode and said pair of sub-current electrodes includes alinear portion; the linear portion in said main current electrode andthe linear portion in said pair of sub-current electrodes areelectrically interconnected with connecting portions which extend in avertical direction to the electrodes; positions where said twoconnecting portions and said main current electrode intersect are set onopposite sides of a position of said main current electrodecorresponding to a central position where the neutral atoms arecaptured. By using an electrode according to such an embodiment, it canbe utilized as an S-shaped electrode which will be later described, sothat neutral atoms can be effectively captured and the whole device canbe miniaturized.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein one or more ofsaid main current electrode and said pair of sub-current electrodesinclude: a linear portion; and portions bending downwards (in a negativedirection of the y-axis) at one or both ends of said linear portion.Specifically, one shown in FIG. 9 can be mentioned. Having the portionsbending downwards, it is made possible to enhance an x-directed biasmagnetic field at the vicinity of the zero point, so that an externalmagnetic field can be reduced, and it is consequently made possible toreduce applied current for a device while miniaturizing the wholedevice.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices, wherein one or more ofthe said main current electrode and said pair of sub-current electrodesinclude: a linear portion; and a U-shaped portion having a linearportion and bending portions at both ends of said linear portion. SuchU-shaped portions are provided on the x-z plane, and one including twolinear portions parallel to the x-axis and a linear portion parallel tothe z-axis while connected to said portions parallel to the x-axis canbe mentioned. Since it includes such electrode portions, a z-directedmagnetic field can be enhanced by a magnetic field generated by theportions parallel to the x-axis, so that an external magnetic field isreduced, and it is consequently made possible to reduce applied currentfor a device while miniaturizing the whole device.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices having an optical beamgenerating portion for irradiating optical beams into a multipolemagnetic field generated by said multipole-magnetic field-generatingelectrode. Having an optical beam generating portion, the neutral atomtrapping device can function as so-called “magneto-optical trap”. Whilea wavelength within a range between visible and near infrared, forexample, can be appropriately used as a wavelength of the lightcomposing the light beam, the absorbed wavelength of light depends onthe type of the neutral atom to be captured, so that appropriatewavelength may be used according to the neutral atom to be captured. Forexample, light with wavelength of 780 nm or 795 nm may be used whenrubidium atoms are to be captured, and light with wavelength of 852 nmor 894 nm may be used when cesium atoms are to be captured.

Publicly-known elements in magneto-optical traps and magnetic traps canbe appropriately adopted for the neutral atom trapping device of thepresent invention. The neutral atom trapping devices themselves arepublicly-known, and may appropriately include: vacuum pumps for vacuumdevice, a vacuum chamber with electrode storage capacity, an atom-beamgenerating portion generating neutral atoms, a magnetic field generatingportion (electrode) for applying various magnetic fields, mirrors,detectors, and the like. When the neutral atom trapping device of thepresent invention is used to deposit neutral atoms on samples, a samplestand for loading samples, a control device for controlling the positionof a sample stand, an electric field generation device for controllingdirections of atom beams, a magnetic field generating device forcontrolling directions of atom beams, a light source for controllingdirections of atom beams, and the like may be appropriately included.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices which is provided with: anoptical beam generating portion for irradiating optical beams from fourdirections along a symmetric axis of a magnetic quadrupole componentinto a multipole magnetic field generated by said multipole-magneticfield-generating electrode; and a total reflection mirror; and whichfunctions as a surface magneto-optical trap.

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is any one of theabove-mentioned neutral atom trapping devices which has an optical beamgenerating portion for irradiating optical beams from six directionsalong a symmetric axis of a magnetic quadrupole component into amulti-pole magnetic field generated by said multi-pole magnetic fieldgenerating electrode without having a total reflection mirror.Hereinafter, how the above-mentioned effect can be achieved with theabove-mentioned arrangement will be described.

A magnetic field on the x-y plane generated by an electric currentflowing through a single central conductor can be approximated by aquadrupole magnetic field at the vicinity of the trap center Q (0, y₀)as shown in FIG. 1( b). However, as the distance from the trap centerincreases, it deviates from the quadrupole. It is easy to understand thebehavior of this magnetic field by considering that higher ordermulti-pole magnetic fields are superposed with one another at the trapcenter.

Hereinafter, phenomena in two dimensions will be described in order tointelligibly explain the characteristics of the invention. FIGS. 5(a)-5(c) schematically illustrate, a magnetic field (FIG. 1( a)) formedby a single linear current I₁ near the trap center (the zero point Q) towhich a multipole expansion is performed to show magnetic multipolecomponents of dipole, quadrupole and hexapole thereof. FIG. 5( a) showsthe condition of a dipole magnetic field, FIG. 5( b) shows that of aquadrupole magnetic field, and FIG. 5( c) shows that of a hexapolemagnetic field. In FIGS. 5( a)-5(c), typical magnetic field lines areindicated by arrows and the axis of symmetry on a magnetic field isshown by double-dash-lines. Higher order multipoles beyond octapoles canalso be analogized in the same way as in FIG. 5( a)-FIG. 5( c). Themagnetic field shown in FIG. 1( a) can be expressed as an overlapping ofall of those multipoles. The contribution of each component around thezero point Q decreases in order of dipole, quadrupole and hexapolerespectively, and by adding a certain x-directed uniform bias magneticfield from outside, a dipole component gets cancelled out so that aquadrupole component appears most remarkably. Such a situation is themagnetic field shown in FIG. 1( b). The ideal quadrupole magnetic fieldshown in FIG. 5( b) is desirable in order to form a magneto-opticaltrap. However, as shown in FIG. 1( b) the far the magnetic field drawsapart from the point Q, the more it deviates from the ideal quadrupolecomponent field due to the contribution of higher-order multipolesbeyond hexapoles.

On the one hand, in the magnetic field shown in FIG. 1( a) and/or (b),for the exception of the extreme vicinity of electric current, theactual far-field profile of a magnetic field is relatively simple. Thus,it is clear that the higher the order of multi poles, the smaller thecontribution to the far-field profile of higher order multi-poles.Therefore, it is sufficient to pay attention to the component withrelatively lower poles among the higher order multi-poles, such as thatof hexapole or, at most, octapole; especially that of hexapole is mostimportant. Therefore, it is conceived that the form of the magneticfield near the trap center Q is to be improved by selectivelyeliminating the component of the hexapole magnetic field generated nearthe trap center Q.

A procedure of eliminating a hexapole component is as follows: FIG. 6schematically represents an overlapping view of the quadrupole magneticfield with the hexapole magnetic field generated around the trap centerQ (0, y₀) by electric current I₁ flowing through the central conductor.In the drawing, the hatched portion (region A) represents a region wherethe hexapole magnetic field lines are turning clockwise with respect toQ and the painted portion (region B) represents a region where thequadrupole field lines are turning clockwise with respect to Q. Thewhite background (region C) represents a region in which the magneticfield lines for both quadrupole and hexapole are turningcounter-clockwise with respect to Q. Provided with the angle θ (deg) asshown in FIG. 6, for instance, the magnetic field lines for bothquadrupole and hexapole are turning clockwise in the region of−30°<θ<30°, and in the region of 30°<θ<45°, the magnetic field lines forquadrupole are turning clockwise while that of the hexapole are turningcounter-clockwise.

If the linear current is in the direction other than θ=0°, it has onlyto consider that the whole region A or B is rotated by θ in accordancewith the above direction. When rotated by θ=±90°, the direction of themagnetic field lines in the region B and the other regions besides Bexchanges, and when superposed on the original quadrupole magneticfield, they cancel each other out completely; so that the quadrupoledisappears. In addition, the hexapole rotates reversely when rotated atθ=±60°, and they cancel each other out and disappear when superposedwith the original hexapole.

Here, in addition to the electric current I₁ flowing through the centralconductor, it is considered that a pair of linear currents I₂ is addedon the x-axis (i.e., three dimensionally in parallel to the z-axis onthe x-z plane). FIG. 4 describes the condition in which three linearconductors in parallel to the z-axis are set on the x-z plane inparallel to each other at equal intervals. Although the direct currentwith the positive direction on the z-axis is provided to the threeconductors, it is supposed that different electric currents I₁ and I₂can be respectively provided to the central conductor and a pair of theconductors set on both sides. When a total reflection mirror is locatedon the x-z plane, since the conductors are placed within or below thex-z plane, there is to be no concern that the optical lasers be blocked,thus it is favorable for composing a surface magneto-optical trap. WhenI₂ is placed on the region at −30°<θ<30°, both the quadrupole and thehexapole are strengthened, when I₂ is placed on the region at 30°<θ<45°or at −30°<θ<−45° as shown in FIG. 6, the quadrupole is enhanced whilethe hexapole counteracts and gets weakened. Therefore, by selectivelychoosing the magnitude/strength of I₁ and I₂, the hexapole can becompletely eliminated. Although it is not drawn in FIG. 6, the effect ofcanceling out the octapole can also be obtained in the region at30°<θ<45° or at −30°<θ<−45°. According to the detailed calculation,although it is known that both the hexapole and the octapole can becompletely eliminated simultaneously at θ=±45°, the quadrupole cannot bestrengthened under this condition; therefore, it is preferable that theθ is set to be within ±45°.

Since the previous method using the planar conductor is to flow electriccurrent even at the region at −30°<θ<30°, both the quadrupole and thehexapole are enhanced. And in order to cancel out the enhanced hexapole,the width of the central conductor needs to be widened so that itbroadly projects towards the region at θ>30°; accordingly, there arisesthe necessity for providing more electric current. On the one hand, aneutral atom trapping device relating to the first aspect of the presentinvention is able to selectively strengthen the quadrupole whileattenuating the hexapole; as a result, it is enabled to obtain the sameeffect as compared to the prior art while using less electric current.

As an actual implementation, the three conductors cannot be madeinfinitely long, so that having to be vertically bent downwards (to thenegative direction on the y-axis) at a certain length; and they areconsidered to be connected to the external part of the electric currentsources via a feed-through for ultrahigh vacuum. In this case, since thex-directed bias magnetic field near the point Q is enhanced by electriccurrent at the vertically bent portions on the ends of the conductors,it is enabled to weaken the current value required for generating a biasmagnetic field.

When the wiring as shown in FIG. 4 is used, it is preferable that aninhomogeneous magnetic field is added from outside towards the z-axis inorder to capture neutral atoms three dimensionally. However, it ispossible to omit adding a z-directed magnetic field from outside bymodifying one or more of the three conductors into a U-shape therebyresembling the similar structure as in FIG. 2( b).

In addition, as it is possible to adjust the each provided electriccurrent independently, for instance, by placing multiple electriccurrents on the x-z plane with inconstant or constant intervals, or byarranging them on a cylindrical surface with the zero-point Q as itscenter; as a result, an electric wiring, which enables to cancel outspecified arbitral multi-poles or to strengthen only the specifiedmulti-poles, can be obtained via numerical calculation by using, forinstance, a pattern-matching method. However, when mounting as aneutral-atom trapping device—since it is ideal that the structure be assimple as possible while obtaining the greatest effect—merely using thethree conductors, as mentioned above, may be a realistic mountingpattern.

[A Configuration to Make Sub-Current onto a Capturing Region]

A preferred embodiment of a neutral atom trapping device according tothe first aspect of the present invention is provided with: amultipole-magnetic field-generating electrode which includes; a maincurrent electrode where a main current flows; and a sub-currentelectrode which is provided on an opposite side of said main currentelectrode through a region where neutral atoms are captured and whichincludes a linear portion where a sub-current flows. The neutral atomtrapping device of this embodiment also functions in the same way asdescribed above, so that the sub-current electrode enhances the magneticquadrupole component while attenuating a magnetic hexapole component. Itis to be noted that the neutral atom trapping device according to thisembodiment can appropriately adopt each arrangement mentioned above. Amore preferred embodiment of a neutral atom trapping device according tothis embodiment is a neutral atom trapping device, wherein saidsub-current electrode includes a linear portion which is provided abovesaid main current electrode through a region where neutral atoms arecaptured, curved portions extending downwards from both ends of saidlinear portion; and a linear portion extending downwards from saidcurved portions. More specifically, it is any one of the above-mentionedneutral atom trapping devices, wherein said sub-current electrodeincludes: a linear portion which is provided above said main currentelectrode through a region where neutral atoms are captured;semicircular portions extending downwards from both sides of said linearportion; and linear portions extending downwards from bottom ends ofsaid semicircular portions. Such a curved portion and semicircularportion contribute(s) to generating a z-directed magnetic field besideseffectively detouring a laser light. Furthermore, the portion extendingdownwards contributes towards generating an x-directed magnetic field.Thus, since an external magnetic field can be reduced, the whole devicecan be miniaturized besides reducing current impressed to the device.

The electrode portion with this aspect is shown in FIG. 6. That is,besides placing the main current electrode (I₁), placing the linearsub-current electrodes in the direction at θ=180°, as shown in FIG. 6,I₃, also enables to obtain the effect in which the quadrupole isenhanced while the hexapole is attenuated. In this case, although theoctapole magnetic field gets strengthened, a magnetic field generated byI₃ also has the effect of enhancing an x-directed bias magnetic field,hence convenient depending upon intended purposes. For instance, byusing I₃, since the x-directed bias magnetic field from outside is to beno longer necessary (i.e., the bias magnetic field can be providedautomatically), it is suitable for miniaturizing a neutral atom trappingdevice. When laser beams are propagated from above, there might be asituation in which a conductor blocks a portion of laser beams. However,when composing a surface magneto-optical trap, it will not be a problemsince there is no need to propagate laser beams vertically from above.Further, a trapping device for neutral atom trap relating to thisaspect, it can have a pair of the sub-current electrodes as indicated inI₂ but usually it is not required as explained above. The principle ofthe configuration, in which the sub-current is placed above the trappingregion, is explained below.

When transparent conductive oxides, for instance, are used for aconductive material, the arrangement for irradiating the laser beamsthrough an electrode is also possible. However, it is more desirable todevise the placement so as not to block the laser beams. FIG. 7 is aconceptual diagram showing an example of a wiring which does not blockthe leaser beams. In FIG. 7, “2” indicates the main current electrodeand “3” indicates the electrode for sub-current. As indicated in FIG. 7,when the electric current I′ flows through along the conductor in theorder of a→b→c→d→e→f; then, the quadrupole on the point Q getsstrengthened while the hexapole is to be canceled out by the electriccurrent flowing in-between the principle part c-d. The b-c and d-eportions which extend downwardly in the semicircular portion from bothtips of c-d are bent in order for the laser beams to detour, and alsoproduce the effect contributing to the formation of a z-directedmagnetic field as a part of anti-Helmholtz coils as shown in FIG. 2( a).Furthermore, a-b and e-f parts extending vertically downwardlycontribute to forming an x-directed bias electric field. In addition, aneutral atom device relating to this aspect can appropriately adopt theabove mentioned configuration.

[S-Shaped Electrode]

A neutral atom trapping device according to the second aspect of thepresent invention is one that by bending Ioffe bars, which have beenZ-shaped, in a right angle to form an S-shaped structure, the generationof a bias magnetic field component in the z-direction can be reduced,the curvature at a z-directed magnetic field can be increased, a biasmagnetic field in the x-direction can be enhanced. As a result, it ismade possible to obtain the same degree of ability to capture neutralatoms with lesser electric current than the prior art. Namely, a neutralatom trapping device according to the second aspect of the presentinvention is provided with: when a point of origin is set at a pointbelow a central portion where neutral atoms are captured, a z-axis isset to a direction of the linear portion of a multipole-magneticfield-generating electrode near a center where said neutral atoms arecaptured and a center where the neutral atoms are captured is providedon the y-axis, said multipole-magnetic field-generating electrodeincludes; a linear portion extending along the z-axis through said pointof origin; a portion extending in a direction parallel to the x-axisfrom said linear portion; and a portion parallel to the z-axis extendingfrom the two portions extending in a direction parallel to the x-axis.As described above, by forming an S-shaped structure by further bendingthe Ioffe bar of a Z-shaped conductor in right angle, generation of az-directed bias magnetic field component can be reduced whilereinforcing the curvature in a z-directed magnetic field, as well asreinforcing an x-directed bias magnetic field. As a result, it is madepossible to obtain the same degree of ability to capture neutral atomswith lesser electric current than the prior art.

FIG. 8 is a conceptual diagram showing a new conductor in which botharms extending towards the x-axis (the Ioffe bars), which is used oftenfor surface magnetic traps in a conventional Z-shaped conductor, arebent in the z-direction. This S-shaped conductor is provided with: aportion A which is a part extending along the z-axis through the pointof origin; a portion B which is a part extending (a little) in parallelto the x-axis from both ends of the portion A; and a portion C which isa (long) portion further bending at both ends of portion B and thenextending in parallel to the z-axis. A quadrupole magnetic field isformed near the point Q by overlapping the externally provided biasmagnetic field directing in the x-axis with the electric current passingthrough the portion A; and a magnetic trap is formed when a z-directednon-uniform magnetic field is formed on the point Q by the electriccurrent flowing through the portion B.

The most significant difference between the S-shaped conductor in thepresent invention and the conventional Z-shaped conductor in the priorart resides in the length of the portions corresponding to the portionB. Because the portion corresponding to the portion B was elongated inx-direction in the prior art method (a Z-shaped conductor), thecomponent for a z-directed bias magnetic field formation with thepositive direction (a dipole magnetic field) is strongly generated;therefore it was required to add the z-directed strong bias magneticfield with the negative direction from outside in order to cancel itout. In addition, because the portion corresponding to the portion B isa long linear conductor, the required curvature of the magnetic fieldfor confining atoms in the z-direction, was small. On the contrary,since the present invention with the S-shaped conductor enables toshorten the portion B adequately, it can regulate the bias magneticfield with the positive direction on the z-axis; thereby, adding astrong z-directed bias magnetic field from outside becomes no longernecessary. Furthermore, since it can shorten the portion B adequately,the curvature of the magnetic field generated in the z-directionincreases (the strength of the magnetic field for the infinitely longconductor is inversely proportional to the distance from electriccurrent; on the other hand, the strength of the magnetic field for theshort conductor (an infinitesimal electric current) is inverselyproportional to the squared distance from electric current), thereby itenables to obtain deeper trapping potentials. In addition, the specificlength of the portion B varies greatly depending upon: the scale of aneutral atom trap, the external magnetic field, the desired precision,etc. In any case, it is enabled to shorten the portion B as compared tothe conventional Z-shaped conductor in prior art. An approximate valueof 1-5 mm can be used as a specific length for the portion B.

In the present invention concerning the S-shaped conductor, by adding aportion C which was absent in the conventional Z-shaped conductor in theprior art, the x-directed bias magnetic field around the point Q getsenhanced by the electric current running through this portion. Thus, itis enabled to capture atoms effectively with less electric current. Bycomposing a surface magnetic trap, etc., using the S-shaped conductor,enables to compose a magnetic trap with smaller electricity as comparedto using the conventional Z-shape conductor in prior art.

In the magnetic trap, the symmetry of the magnetic field distribution isnot so important; so that a design concerned with higher ordermultipoles is not needed as in the present invention according to thefirst aspect of a neutral atom trapping device. However, if theprojected angle between the two vectors from point Q to two of theportions C is more than 90°, it enables to enhance the quadrupolemagnetic field around the point Q by the electric current flowing thoughthe portions C; hence preferable.

A part of the conductor, where the sub-current I₂ flows and which isadopted in the first aspect of the present invention of a neutral atomtrapping device, can also be served as the portion C of the S-shapedconductor adopted in the second aspect of the current invention of aneutral atom trapping device. Therefore, the effect which eachconfiguration brings by can be obtained simultaneously by adopting theseconfigurations.

By integrating the magneto-optical trap, as explained in the firstand/or second aspect of the present invention of a neutral atom trap,with a magnetic trap; it becomes suitable for further miniaturization inthe course of the actual implementation. FIG. 9 is a conceptual diagramshowing an example in which the electric current I₂ flowing through apair of sub-current electrodes (conductors) in the first aspect of thepresent invention of a neutral atom trapping device also serves as theportion C in the second aspect of the present invention of a neutralatom trapping device. When the present invention of a neutral atomtrapping device is used as a surface magneto-optical trap of a hexapolecompensated type, only the electric current I₁ and I₂ are required; whenit is used as a S-shaped surface magnetic trap, only the electriccurrent I₃ is required. In addition, although the three conductors areelectrically shortened each other by the Ioffe bars in FIG. 9, if eachconductor is driven independently with an independent current source asshown in FIG. 9, then, due to the electric energy-conversion law, thereis to be no hindrance in terms of the function as long as it is used asa hexapole compensating surface magneto-optical trap wherein no electriccurrent flows through the Ioffe bars.

When only the structure of the conventional conductor as shown in FIG. 2is used, the occupied area of a whole conductor including the wiringparts for applying electric current on the x-z plane becomesconsiderably large. But in the structure shown in FIG. 9, since most ofthe parts are concentrated in a small area along the z-axis, the totaloccupied area hardly differs from FIG. 4, in that it is easy tointegrate and becomes suitable for miniaturization.

In addition, since a steeper magnetic gradient is required in a magnetictrap than in a magneto-optical trap, it is commonly so designed that thecenter Q in the trap comes as close to the conductor as possible, assuch, the projected angle from the two conductors, where the subsidiarycurrent I₂ is applied, to the point Q on the magnetic trap becomeslarger than 90°, thereby the quadrupole magnetic field on the x-y planeis enhanced; as a result, it becomes more desirable.

FIG. 10 is a conceptual diagram of the surface magneto-optical trap. Asshown in FIG. 10, the neutral atom trapping device according to such anembodiment sets up a total reflection mirror (11) on the x-z planeforming the electrode (12) thereon. Furthermore, although the electrode(12) is illustrated in FIG. 9, the electrode structure as shown abovecan appropriately be adopted for use. Also, impressing the bias magneticfield (B_(0x)) towards the x-axis, and the four lasers (13 a, 13 b, 13 cand 13 d) are to be propagated towards the center of the captured atomiccloud (14).

EXAMPLE 1 —Analasys for Equal Magnetic Potentials Wherein Sub-Currentsare Placed in Parallel to Main Current—

FIGS. 11( a) and 11(b) show calculation results comparing a shape oftwo-dimensional magnetic field generated by the main current I₁ alone,with that generated by canceling a hexapole magnetic field using themain electric current I₁ together with the sub-current I₂. FIGS. 11( a)and 11(b) are graphs showing the calculation result comparing thetwo-dimensional magnetic field generated by the main current I₁ alone,with that generated by the cancellation process of the hexapole magneticfield when both the main current I₁ and the sub-current I₂ are used.FIG. 11( a) shows a magnetic field generated by the main current I₁alone, FIG. 11( b) shows the behavior of the magnetic field structure intwo dimensions generated by completely canceling the hexapole magneticfield using the main current I₁ together with the sub-current I₂. FIGS.11( a) and 11(b) depict equal magnetic potential lines (lines whichcontinuously connect the positions of equal magnetic potential |B|)instead of magnetic field lines.

In FIG. 11( a), I₁ is calculated as 7.2 A and in FIG. 11( b), the maincurrent I₁ and the sub-current I₂ are calculated as 4.8 A and 10.8 Arespectably. In an ideal quadrupole magnetic field, the equal magneticpotential lines become concentric with equal intervals to each other. Asbeing evident in FIGS. 11( a) and 11(b), near the center of the graph,FIG. 11( b) which involves sub current becomes closer to the idealquadrupole magnetic field than that in FIG. 11( a).

A neutral atom trapping device of the present invention can be used forcapturing and cooling neutral atoms near the surface of a planesubstrate placed in an ultrahigh vacuum chamber by using both a magneticfield generated by the electric current flowing through a conductorwithin or on a plane substrate and a magnetic field provided fromoutside of a substrate if necessary.

According to a neutral atom trapping device of the present invention ofwith the abilities to capture neutral atoms and cool them, it mayeffectively be used for: a Bose-Einstein condensation-generation device;a gravimeter; an accelerometer, a gyroscope using an atom-waveinterferometer; a quantum-information processing device using neutralatoms; a quantum communication device; an atom laser generator, an atomlithography or atomic clock, etc.

1. A neutral atom trapping device, comprising: a multipole-magneticfield-generating electrode which includes; an electrode for main currentwhere a main current flows, and a pair of sub-current electrodes, wherea sub-current flows, located in parallel to both sides of said electrodefor main current.
 2. The neutral atom trapping device according to claim1, wherein said sub-current electrodes function to enhance a magneticquadrupole component while attenuating a magnetic hexapole component ina region where neutral atoms are captured.
 3. The neutral atom trappingdevice according to claim 1, wherein each of said main current electrodeand said pair of sub-current electrodes includes a linear portion. 4.The neutral atom trapping device according to claim 1, wherein each ofsaid main current electrode and said pair of sub-current electrodesincludes a linear portion, and the linear portion in said main currentelectrode and the linear portion in said pair of sub-current electrodesare electrically interconnected with connecting portions which extend ina vertical direction to the electrodes.
 5. The neutral atom trappingdevice according to claim 1, wherein: each of said main currentelectrode and said pair of sub-current electrodes includes a linearportion; the linear portion in said main current electrode and thelinear portion in said pair of sub-current electrodes are electricallyinterconnected with connecting portions which extend in a verticaldirection to the electrodes; positions where said two connectingportions and said main current electrode intersect are set on oppositesides of a position of said main current electrode corresponding to acentral position where the neutral atoms are captured.
 6. The neutralatom trapping device according to claim 1, wherein one or more of saidmain current electrode and said pair of sub-current electrodes include:a linear portion; and portions bending at one or both ends of saidlinear portion towards the opposite of the central position whereneutral atoms are captured.
 7. The neutral atom trapping deviceaccording to claim 1, wherein one or more of the said main currentelectrode and said pair of sub-current electrodes include: a linearportion; and U-shaped portions having a linear portion and bendingportions at both ends of said linear portion.
 8. The neutral atomtrapping device according to claim 1, further comprising an optical beamgenerating portion for irradiating optical beams into a multipolemagnetic field generated by said multipole-magnetic field-generatingelectrode.
 9. The neutral atom trapping device according to claim 1,which functions as a surface magneto-optical trap, further comprising:an optical beam generating portion for irradiating optical beams fromfour directions along a symmetric axis of a magnetic quadrupolecomponent into a multipole magnetic field generated by saidmultipole-magnetic field-generating electrode; and a total reflectionmirror.
 10. The neutral atom trapping device according to claim 1,further comprising an optical beam generating portion for irradiatingoptical beams from six directions along a symmetric axis of a magneticquadrupole component into a multipole magnetic field generated by saidmultipole-magnetic field-generating electrode, but not comprising atotal reflection mirror.
 11. A neutral atom trapping device comprising:a multipole-magnetic field-generating electrode which includes; a maincurrent electrode where a main current flows; and a sub-currentelectrode which is provided on an opposite side of said main currentelectrode through a region where neutral atoms are captured and whichincludes a linear portion where a sub-current flows.
 12. The neutralatom trapping device according to claim 11, wherein said sub-currentelectrode further including; a linear portion which is provided on anopposite side of said main current electrode through a region whereneutral atoms are captured, curved portions extending from both ends ofsaid linear portion towards the main current electrode; a linear portionextending from said curved portion to an opposite side of a centralposition where neutral atoms are captured.
 13. The neutral atom trappingdevice according to claim 11, wherein said sub-current electrode furtherincluding; a linear portion which is provided on an opposite side ofsaid main current electrode through a region where neutral atoms arecaptured, a semicircular portion extending from said linear portiontowards the main current electrode; a linear portion extending from abottom end of said semicircular portion to an opposite side of a centralposition where neutral atoms are captured.
 14. The neutral atom trappingdevice according to claim 11, wherein when a point of origin is set at aposition of the main current electrode corresponding to a centralportion where neutral atoms are captured, a z-axis is set to a directionof the linear portion of a multipole-magnetic field-generating electrodenear a center where said neutral atoms are captured and a center wherethe neutral atoms are captured is provided on the y-axis, saidmultipole-magnetic field-generating electrode includes; a linear portionextending along the z-axis through said point of origin; a portionextending in a direction parallel to the x-axis from said linearportion; and a portion parallel to the z-axis extending from the twoportions extending in a direction parallel to the x-axis.